Ionomeric polyvinyl butyral

ABSTRACT

Polyvinyl butyral resin containing a modification-promoting amount of up to about 15 mole % ionomeric groups which are preferably the metal sulfonate salt of an aldehyde chemically combined with oxygen atoms of adjacent precursor vinyl alcohol groups. Such resin is prepared from a precursor PVOH containing chemically bound ionic acid groups.

BACKGROUND OF THE INVENTION

This invention relates to chemically modified polyvinyl butyral resinand a precursor used in its synthesis.

Plasticized polyvinyl butyral sheet is very well known as an interlayerfor use with glass or rigid plastic panels in laminated safety glazingassemblies. The polyvinyl butyral resin is more particularly partialpolyvinyl butyral insofar as containing about 15 to about 30 percent byweight residual hydroxyl groups which promote adherence of the sheet tothe glass or plastic. Such polyvinyl butyral or partial polyvinylbutyral, (interchangeably referred to as PVB), is conventionallyprepared by partially acetalizing polyvinyl alcohol (PVOH) withbutyraldehyde. The PVB is then conventionally mixed with plasticizer andmelt processed into sheeting which is usually collected and stored inroll form before use. In use, sections for individual glazing units arecut from the roll, placed between or adjacent one or more laminatingpanels and the sandwich pressed together in an autoclave at elevatedtemperature and pressure to form the laminate.

Plasticized PVB sheet used in this way inherently tends to stick toitself (sometimes called "blocking") at ambient temperatures typicallyencountered during storage before laminating. Expensive precautions havebeen taken to prevent this. For example, the sheet has been transportedand stored at low refrigeration temperatures, or interleaved withpolyethylene film or dusted between facing layers with sodiumbicarbonate. It has been and continues to be very desirable to alleviatethis blocking problem associated with plasticized PVB sheet.

Another problem occurs during laminating when incomplete contact existsbetween the PVB sheet and the contiguous laminating panel. This iscaused by thickness tolerance variations in the sheet and laminatingpanel and results in visually apparent, local, unlaminated patchesappearing as bubbles. In the past, when these patches appeared onlaminating lines the problem was overcome by extending the autoclavecycle to heat the sheet to a higher temperature to promote greaterpolymer flow. But this undesirably results in increased energy costs andimposes a capacity-affecting limitation on laminating lines. Tailoringthe sheet polymer modulus to promote slight additional flow into anuneven area of the gap between the sheet and opposing panel couldalleviate the problem. But this works at cross purposes with minimizingsticking of the sheet to itself before laminating. In other words,reducing modulus to promote flow during laminating will undesirablyincrease stickiness at ambient temperature. On the other hand,increasing ambient temperature modulus to stiffen the sheet enough toresist sticking will decrease flow during laminating. Yet optimum flowduring laminating is increasingly important in vehicle glazingapplications as the amount of glass per vehicle is increased.

It would be very desirable to simultaneously favorably influence each ofthese problem areas associated with use of plasticized PVB sheet inlaminated safety glazings and avoid performance trade-offs which haveoccurred in reducing one problem at the expense of the other. To thebest of our knowledge, however, such corrections have not been providedin the prior art.

SUMMARY OF THE INVENTION

Now improvements have been made to increase the ambient temperatureresistance of PVB sheet to blocking while simultaneously improving itsflow during lamination.

Accordingly, a principal object of this invention is to chemicallymodify PVB resin so that when used as a sheet for safety glazings theusual stack or roll sticking and laminate flow problems are reduced oreliminated.

A specific object is to provide a polyblend of PVB's for shaping into aglazing sheet.

Another object is to achieve the foregoing objects without significantlydeparting from conventional ways of synthesizing PVB resin, formingplasticized PVB sheet and laminating such sheet with other panels toform a safety glazing.

These and other objects are accomplished by providing a new species ofPVB resin which contains ionomeric groups capable of providing thermallyreversible ionic crosslinks ("ionomeric PVB" abbreviated as "IPVB").More specifically, at low ambient temperatures (ca 40°-60° C.) wheresticking problems occur, such temperature-dependent ionic crosslinks areinherently established to promote block resistance whereas at elevatedlaminating temperatures where flow is important, such linkages areinherently severed to promote flow into uneven portions of the gapbetween the sheet and opposing laminating panel(s).

The IPVB resin contains a modification-promoting amount of ionomericgroups chemically combined therein, preferably to oxygen atoms ofadjacent precursor vinyl alcohol groups. Such ionomeric groups arepreferably present at up to about 15 and most preferably about 2 toabout 5 mole percent. The ionomeric groups are bound into the PVBpreferably through the reaction between an aldehyde group and twohydroxyl groups. A particularly preferred ionomeric group is the metalsulfonate salt of an aldehyde. Polyvinyl alcohol containing chemicallybound ionic acidic groups is the precursor for ionomeric PVB resin.

DETAILED DESCRIPTION OF THE INVENTION

IPVB resin is an ionized copolymer comprising a major component of anon-ionic backbone of partial PVB containing 65-95 weight percent vinylbutyral units, 15 to 30 weight percent hydroxyl groups calculated asvinyl alcohol and 0 to 5 percent vinyl ester units (calculated as vinylacetate) and a minor component of an ionizable or ionic comonomer. Thelatter minor component distinguishes IPVB from partial PVB traditionallyused in sheeting for glazing applications and is provided by chemicallymodifying the polyvinyl alcohol in conjunction with acetalization withbutyraldehyde to form the non-ionic partial PVB resin backbone. PVOHmodification is done through attachment of ionic acidic groups to a pairof hydroxyl groups of the PVOH to form a modified PVOH precursor to theIPVB. This modification is done by the chemical condensation reaction ofPVOH and, preferably, an ionic aldehyde. This is illustrated by thefollowing reaction where the acidic groups are ionic sulfonated benzalgroups obtained by reacting PVOH with the sodium salt of 2-formylbenzene sulfonic acid (BSNA) having the following structural formula:##STR1## The PVOH reaction in the presence of HN0₃ catalyst isillustrated as follows: ##STR2##

Usable PVOH (either a single grade or two or more grades blendedtogether) are commercially available, for example from Air Products andChemicals, Inc. or E. I. du Pont de Nemours & Co., Inc. They arecharacterized by degree of polymerization (DP) which ranges from about350 to 2500 to provide PVOH molecular weight from 15,000 to 110,000. Asan optional feature, low molecular weight PVOH having a DP of 350 to 800and a molecular weight of about 15,000 to about 35,000 can be used whencertain ionomeric components (described hereinafter) are used and thePVOH-ionomeric and acetalization reactions are conducted at lowtemperature below 20° C. Such low molecular weight PVOH hastraditionally not been sufficiently reactive with butyraldehyde to makePVB due to the physical nature of the material which causes it toagglomerate. Its use is desirable since in furtherance of the objects ofthis invention the correspondingly low molecular weight PVB formed willbe "softer" and flow better at laminating temperatures while, due to thepresence of ionomeric groups, being stiffer and more block resistant atambient temperatures in comparison with results using all medium or highmolecular weight PVOH (and resulting high molecular weight PVB). Mediumto high molecular weight PVOH's have a DP of about 810 to 15,000 and amolecular weight of about 35,500 to about 110,000.

The modified PVOH containing the ionic acid groups is acetalized underaqueous or solvent acetalization conditions by reacting the PVOHprecursor with butyraldehyde in the presence of an acid catalyst. Theacetalized reaction product is then neutralized to form the polymersalt. Neutralization need not be complete in that some unneutralizedproduct in acid form can be present but neutralization has to besufficient to give the ionic associations in use which are later morecompletely described. Neutralization is effected by adding metal ionssuch as Na⁺, K⁺, Ca⁺⁺, Ba⁺⁺, Zn⁺⁺, NH₄ ⁺ etc. to the reaction medium.Using the precursor shown above, this is illustrated by the followingreactions to form one species of IPVB according to the invention:##STR3## The ionomeric groups of the foregoing IPVB species are presentas the sodium salt of sulfonated polyvinyl benzal chemically bound tooxygen atoms of adjacent precursor vinyl alcohol groups formed initiallythrough reaction between a CHO aldehyde group of the BSNA ionomericconstituent and two hydroxyl groups on a PVOH molecule.

In a solvent process acetalization occurs in the presence of acidcatalyst and sufficient solvent to dissolve the modified PVB formed andproduce a homogeneous solution at the end of acetalization. The modifiedPVB is separated from solution by precipitation of solid particles withwater which are then washed, neutralized and dried. Solvents used arelower aliphatic alcohols, such as ethanol.

In an aqueous process, acetalization occurs by adding butyraldehyde to awater solution of modified PVOH in the presence of an acid catalyst,agitating the mixture to cause the modified PVB to precipitate in finelydivided form and continuing agitation until the reaction mixture hasproceeded to the desired end point.

Acetalization with butyraldehyde in a solvent or aqueous process ispreferably carried out in situ with the PVOH reaction through which theionic acidic groups had previously been attached to the PVOH molecules.This is achieved by adding butyraldehyde directly to the reaction zoneto commence condensation with the modified PVOH after the desired amountof PVOH has reacted with the ionic component. Depending on the chemicalnature of the compound selected to provide the ionomeric bonds, it maybe possible to carry out the ionomeric reaction with PVOH and theacetalization reactions simultaneously. It is preferred, however, toconduct these reactions sequentially in situ when the reaction rate withPVOH of the butyraldehyde significantly exceeds that of the ionomericconstituent, as is the case when a substituted aldehydic aromatic saltis used to provide the ionomeric groups.

The extent of modification of the starting PVOH and the content ofionomeric groups in the IPVB product can vary widely as a function ofthe extent of the reaction of the PVOH and the ionic-containingcomponent. Generally, satisfactory results are obtained when themodified PVOH precursor contains up to about 15, preferably up to about10 and most preferably 2 to 5 mole percent acidic ionic groups and theIPVB resin similarly contains up to about 15, preferably up to about 10and most preferably 2 to 5 mole percent ionomeric groups obtained fromthe modified PVOH precursor.

The temperature of the PVOH reaction should be adequate to reactivelybind the desired amount of acidic ionic groups to the PVOH and will varywith the ionomeric component chosen. When a substituted aldehydicaromatic salt is used, such as the preferred BSNA, the temperaturethroughout the PVOH and acetalization reactions should be below 20° C.,preferably between 8-15 and most preferably 10°-12° C.

The IPVB resin of the invention contains a modification-promoting amountof chemically combined ionomeric groups. Insofar as the chemicalreaction of the ionic component with polyvinyl alcohol to later producethermally reversible crosslinks in PVB formed from such modified PVOH,the ionic component, must contain: i) an active group capable ofinteracting with two hydroxyl groups of a PVOH molecule to chemicallybind the ionic component to the PVOH molecule and ii) an acid groupcapable in use (i.e. after the modified PVOH precursor is acetalizedwith butyraldehyde and neutralized) of forming thermally reversiblepseudo cross-links with equivalent ionomeric groups on other similarlymodified PVOH chains. With this in mind, the chemical structure of theionic component can vary broadly and is represented by the formulaR--XYZ--M where R is the active group referred to above, X and Y aresubstituents of certain of such active groups, E is the acid groupreferred to above and M is a metal cation. More specifically, R equalsan aromatic, aliphatic (straight chained, branched or cyclic) orheterocyclic i) aldehyde (i.e. containing a --CHO group), ii) acid (i.e.containing a --COOH group), iii) acid chloride (i.e. containing a --COClgroup) or iv) isocyanate (i.e. containing an --NCO group), provided thatwhen R is aliphatic it has the configuration (CH₂)_(n) where n is aninteger from 1 to 200; X and Y, which can be the same or different, aresubstituents on the aromatic and heterocyclic forms of i), ii), iii),and iv) and are H or C₁ to C₅ alkyl; Z is SO₃ ⁻, COO⁻, or PO₄ ⁻³, and Mis a cation selected from alkali metals (Group IA in the PeriodicTable), alkaline earth metals (Group IIA of the Periodic Table) andtransition metals selected from zinc, copper and manganese. Alkalimetals are Li, Na, K, Rb, Cs and Fr; alkaline earth metals are Be, Mg,Ca, Sr, Ba, and Ra. The foregoing description of the ionic component isfurther depicted in the following table:

    __________________________________________________________________________                      Aliphatic                                                                     (straight chain/                                            Aromatic          branched or cyclic)                                                                     Heterocyclic                                      __________________________________________________________________________    Aldehyde                                                                             ##STR4##                                                                                  ##STR5##                                                                                ##STR6##                                         Acid                                                                                 ##STR7##                                                                                  ##STR8##                                                                                ##STR9##                                         Acid Chloride                                                                        ##STR10##                                                                                 ##STR11##                                                                               ##STR12##                                        Isocyanate                                                                           ##STR13##                                                                                 ##STR14##                                                                               ##STR15##                                        __________________________________________________________________________

Preferred ionic components are those where R is an aromatic aldehyde, Xand Y are H, Z is SO₃ ⁻ and M is Na⁺. The most preferred ionic componentis the sodium salt of 2-formylbenzene sulfonic acid, i.e. ##STR16##which is commercially available from Aldrich Company or Eastman KodakCompany.

IPVB resin of the invention has use in unblended form (i.e. 100% basis),as a blending concentrate or intermediate in forming sheeting forglazing applications using high molecular weight PVOH as a startingmaterial (DP 1275 to 1600), it may be possible to shape the resultingIPVB directly into sheeting without blending. It is preferably blended,usually in minor amount (less than 50 wt. %), with unmodified partialPVB. The amount of IPVB blended with PVB is dictated by the level ofionomeric groups in the IPVB and the performance properties desired insheet formed from the polyblend. Based on economically reasonablereaction rates with the ionomeric component in forming IPVB, the IPVBcomponent should be present at from about 1 to about 45 weight % (basedon total PVB) in the polyblend. Above 45 wt. % the blend is usually toostiff in flow whereas the improvement in sheet performance properties isnegligible at less than 1 weight %. The preferred level of IPVB in thepolyblend (at 2-5 mole % ionomeric content in the IPVB) is about 10 toabout 30 wt. % and most preferably about 20 wt. %. Typical viscosities(7.5% in methanol at 20° C.) of "soft" flow polyblends according to theinvention (at 10 to 30 wt. % IPVB) are about 100 to 180 cps ascontrasted with about 230 cps for conventional unmodified PVB made fromhigh molecular weight PVOH. A particularly preferred polyblendcomposition at the ratios just referred to comprises a low molecularweight IPVB (i.e. made from PVOH having a molecular weight of from about15,000 to about 35,000) and an unmodified high molecular weight PVB(i.e. made from PVOH having a molecular weight of 50,000 to 110,000).Such a blend particularly optimizes the enhanced performance propertiesin the resulting sheet in that the low molecular weight IPVB promoteshigh temperature flow with reduced blocking while the high molecularweight PVB provides good impact absorption in a laminate containing sucha sheet.

Blending IPVB and PVB can be done with conventional dry blendingequipment before combination with plasticizer or preferably with theplasticizer and optional other additives in a conventional highintensity mixer. The polyblend containing IPVB must be plasticized withfrom about 20 to 80 parts plasticizer per 100 parts of resin blend andmore commonly between 25 and 45 parts for conventional laminated safetyglass use. This latter concentration is generally used when the PVBcomponents of the blend each contain about 15 to about 30 percent vinylalcohol by weight. In general, plasticizers commonly employed are estersof a polybasic acid and a polyhydric alcohol. Particularly suitableplasticizers are triethylene glycol di-(2-ethylbutyrate), dihexyladipate, dioctyl adipate, mixtures of heptyl and nonyl adipates, dibutylsebacate, polymeric plasticizers such as the oil-modified sebacicalkyds, and mixtures of phosphates and adipates such as disclosed inU.S. Pat. No. 3,841,890 and adipates and alkyl benzyl phthalates such asdisclosed in U.S. Pat. No. 4,144,217. Other suitable plasticizers arewell known or will be obvious to those skilled in the art.

The preferred process for preparing PVB sheet according to the inventioninvolves mixing the polyblend with plasticizer as noted above and meltprocessing the plasticized polyblend according to known conventionalprior art techniques to form the sheet. Systems for forming such sheettypically involve extrusion by forcing polymer melt through a sheetingdie having temperature-controlled die lips or by using a die roll systemwhere molten polymer issuing from the die is cast onto a speciallyprepared surface of a roll closely adjacent to the die exit whichimparts the desired surface characteristics to one side of the moltenpolymer. Thus, a roll having a surface with minute peaks and valleysforms a sheet from polymer cast thereon with a rough surface generallyconforming to the valleys and peaks of the surface. Further details ofconstruction of a die roll system are disclosed in U.S. Pat. No.4,035,549, col. 3, line 46 through col. 4 line 4, the content of whichis incorporated herein by reference.

Alternative conventional techniques known to those skilled in the artmay be employed in association with an extrusion process to produce arough surface on either or both sides of the extruding sheet. Theseinvolve the specification and control of one or more of the following:polymer molecular weight distribution, water content of the melt, meltand die exit temperature, die exit geometry etc. Systems describing suchtechniques are disclosed in U.S. Pat. Nos. 2,904,844; 2,909,810;3,994,654; 4,575,540 and published European Application No. 0185,863.

In addition to plasticizers, the PVB sheet may contain other additivessuch as dyes, ultra violet light stabilizers, adhesion control salts,antioxidants and the like. The sheet may also be provided with anintegral, gradient color band during extrusion by known systems astypically disclosed in U.S. Pat. No. 4,316,868. The sheet of theinvention preferably compromises a single layer but could be provided asa multi-layer structure obtained, for example, by coextruding an IPVBlayer with or coating an IPVB layer on a conventional PVB sheet of thesame or different gage thickness. For example, a layer of IPVB could becompression molded onto a conventional PVB sheet or IPVB resin could bedissolved in a solvent, dip or roll-coated onto a conventional sheetfollowed by solvent evaporation, or an IPVB layer could be fused to aconventional sheet during laminating with other panels forming thesafety glazing at elevated temperature and pressure. Alternatively, thecoextruded, coated or fused layer could be formed of a polyblend aspreviously described.

The plasticized PVB sheet containing residual hydroxyl groups has ablock-reducing, flow-promoting amount of ionomeric groups chemicallybound to oxygen atoms of adjacent precursor vinyl alcohol groupsincorporated into the formulation from which it is made. These ionomericgroups provide thermally reversible pseudo cross-links with equivalentionomeric groups on other similarly modified PVOH chains of the partialPVB of the sheet. More specifically, subsequent to acetalization withbutyraldehyde, and after neutralization with NaOH one species of IPVB ofthe invention can be schematically depicted as follows: ##STR17##

Regarding the mechanism of formation of the pseudo crosslinks, it ispostulated that even though, as depicted above, a cation and anion existon each ionomeric group, there is still an affinity of the cation andanion of any particular group for competing cation and anion groups onclosely adjacent ionomeric groups. This can be schematically depicted asfollows where, for simplification, only the ionomeric groups of the IPVBmolecule are shown: ##STR18## It is felt that this affinity results inclusters or aggregates of ionomeric groups which form the thermallyreversible bonds. More specifically, in the absence of sufficient heatenergy to overcome the attraction between adjacent ionomeric groups, thebonds exist to provide the reduced ambient temperature blocking propertyto the sheet of which they are a part. At higher laminatingtemperatures, however, when the sheet is being conformed to the spacebetween closely adjacent layers of glass, (or equivalent) the bondsrupture resulting in increased flow than if (theoretically) they existedat such high temperatures to provide stiffer flow. PVB sheet of theinvention exhibiting (i) improved block resistance has a storage modulusat 40° C. of greater than 6×10⁶ dynes/cm² and (ii) increased flow atlaminating temperatures as represented by a storage modulus at 150° C.of less than 5×10⁵ dynes/cm².

The following tests were conducted on specimens prepared according tospecific examples presented hereinafter.

1.) Near Infrared Spectroscopy (NIR) to measure residual PVOH groups inthe IPVB.

2.) Nuclear Magnetic Resonance Spectroscopy (NMR) and InfraredSpectroscopy (IR) to confirm the presence of ionomeric groups.

3.) Differential Scanning Calorimeter (DSC) to measure polymer glasstransition temperature (Tg).

4.) Storage Modulus using a Rheometrics Dynamic Mechanical Spectrometer.This test measures the amount of energy stored in the polymer as afunction of temperature. The values at 40° and 60° C. (hereinafterG'(40) or (60)) provide an indication of stiffness at ambientsheet-handling temperatures and are used to predict the tendency of thematerial to stick to itself. The value at 150° C. (hereinafter G'(150))provides an indication of flow behavior of the material at higherautoclave temperatures during lamination with glass layer(s).

5.) Haze using a Hunter Haze Meter is a measure of the optical clarityof a standard glass laminate (two glass layers) using a particularplasticized formulation as the interlayer.

6.) Inherent Blocking is the average load in pounds required to separatetwo strips in face-to-face contact of the same sample from themselves.Sample strips are pressed together under 2.5 tons (2.27 t) ram pressurefor 15 minutes. Using an Instron peel tester, a T-type peel test wasthen run on each sample at a crosshead speed of 20 in (50.8 cm) perminute and a chart speed of 5 in (12.7cm) per minute.

Exemplary of the invention are the following specific examples whereinparts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 Synthesis of Ionomeric Polyvinyl Butyral A) Polyvinyl AlcoholPrecursor

Polyvinyl alcohol (PVOH) resin having a residual polyvinyl acetatecontent of less than 2% and a molecular weight of 23,000 was dissolvedwith agitation in water at 85°-90° C. to form an 8.3% solution. 7794.6 gof this PVOH solution was charged to an agitated fluted reactor and itstemperature adjusted to 10°-12° C. To this was added 66.4 g ofo-benzaldehyde sulfonic acid sodium salt (BSNA), and 171.7 g of a 35%solution of nitric acid. The mixture was held at 10°-12° C. for twohours. Analysis of a sample of the reaction product showed 1 to 3 mole %of the acid had chemically combined with the PVOH.

B) Ionomeric Polyvinyl Butyral

At the end of the noted two hours, and while the temperature in thereaction zone was kept at 10°-12° C., 450.6 g of butyraldehyde wereadded to the modified PVOH mixture which was then allowed to react at10°-12° C. with agitation for 4.5-5.5 hrs. The reactor contents werewashed with water once, neutralized with 50% sodium hydroxide to a pH of11.5-12.0, held at this pH for 1.5 hours at room temperature and thenwashed again with water to a final pH of 7.5 to 8.0. The product wasthen filtered and dried to less than 2% moisture. Analysis of theproduct gave the following results:

Residual PVOH groups: 18-19%

BSNA groups in the polymer: 1 to 3 mole %

Tg: 75° C.

EXAMPLE 2 Blending Ionomeric and Conventional PVB's

Conventional PVB available from Monsanto as RB Butvar® resin having aresidual PVOH content of 18.4% was blended with the ionomeric PVB resinof Example 1 at various weight ratios of ionomeric PVB/conventional PVB(IPVB/RB). The blended resins were mixed with dihexyl adipate (DHA) at32.7 parts plasticizer per hundred parts of resin blend. The plasticizedresin blends were compacted in a press at 148.9° C. into "baby cakes".Analytical results obtained were as follows:

    ______________________________________                                                   G' × 10.sup.6                                                                     G' × 10.sup.5                                                                     Inherent Roll                                             (60° C.)                                                                         (150° C.)                                                                        Blocking Avg                                                                           Haze                                  Sample     dynes/cm.sup.2                                                                          dynes/cm.sup.2                                                                          Load (lbs)                                                                             %                                     ______________________________________                                        RB (control)                                                                             4.15      7.12      0.67     1.14                                  10/90 IPVB/RB                                                                            4.03      5.05      0.55     0.93                                  20/80 IPVB/RB                                                                            --        --        0.37     1.19                                  30/70 IPVB/RB                                                                            4.19      3.91      0.32     1.58                                  IPVB (100%)                                                                              6.73      3.05      --       --                                    ______________________________________                                    

The results show that blends containing IPVB are equivalent to the RBControl PVB in ambient temperature stiffness as measured by 60° C.Storage Modulus with 100% IPVB being the stiffest. On the other hand,the blends and pure IPVB exhibit superior flow at higher temperaturesthan the control PVB as measured by 150° C. Storage Modulus. Potentialdecrease in roll blocking of the blends is observed from the averageload to separate two strips of the same sample from each other, i.e.less force is required for the blends than the control. Optical clarityof laminates prepared with interlayer from the blends is comparable tothat of the control.

EXAMPLE 3 Sheet From Blend Containing Ionomeric PVB

A 25/75 IPVB/RB blend was mixed with 32 phr DHA in a non-fluxing(non-melting) high intensity Diosna mixer and, using a 41/2 in (11.4 cm)diameter 32/1 L/D extruder, was extruded into sheeting 30 mils (0.76 mm)thick and 23 in (58.4 cm) wide. Melt temperature was 390°-400° F.(198.9°-204.4° C.). Extrusion was through a die opening onto the surfaceof an adjacent rotating die roll of the type previously describedprovided with internal cooling means to regulate the temperature of adie blade in contact with the polymer melt at about 115.5° C. Meltpressure at the die was 2412-3100 kPa. Sheet issuing from the die rollat about 4.6 m/min was passed into a water cooling bath at 10° C. Thedie lip of the die opening was formed with a compression angle of about4 degrees. Each side of the formed sheet had a rough surface, the bladeside measuring (Rz) 45×10⁻⁵ in or 114×10⁻⁵ cm and the roll side 64×10⁻⁵or 162.6×10⁻⁵ cm. Roughness was measured with a profilometer such asModel C59 Perthometer from Mahr Gage Co., New York.

The following Storage Modulus results (dynes/cm²) at varioustemperatures were obtained on sheet samples prepared as described abovefrom various blends of IPVB/RB.

    ______________________________________                                                 G'        G'        G'      G'                                                (26° C.) ×                                                                 (40° C.) ×                                                                 (60° C.) ×                                                               (150° C.) ×                 Sample   10.sup.7  10.sup.6  10.sup.6                                                                              10.sup.5                                 ______________________________________                                        RB (100%)                                                                              3.27      5.73      4.09    5.98                                     IPVB/RB  4.37      6.12      3.94    6.05                                     (10/90)                                                                       IPVB/RB  4.54      6.76      4.06    4.97                                     (20/80)                                                                       IPVB/RB  5.29      7.72      4.21    4.26                                     (25/75)                                                                       IPVB/RB  5.42      9.35      3.91    3.83                                     (30/70)                                                                       ______________________________________                                    

The above results clearly show that blends containing IPVB are stifferat 26° and 40° C. based on Storage Modulus yet more flowable at 150° C.than the RB control. At 60° C., since the values differ only by about 4%from the control, performance is predicted to be essentially comparable.

EXAMPLE 4 Alternative Ionomeric Constituent

This example shows the use of an acid aldehyde in the synthesis ofionomeric PVB. The aldehyde used was p-carboxybenzaldehyde (CBA) havingthe following chemical structure: ##STR19## Since CBA is ethanolsoluble, the PVOH and acetalization reactions were carried out inethanol.

11 g CBA was dissolved in 280 ml of ethanol in an agitated 2 literreactor and 53.9 g of PVOH (Goshenol NH-18) added to form a PVOH slurryin ethanol. A few drops of concentrated sulfuric acid catalyst wereadded until pH was less than one. The slurry was heated to 75° C. andrefluxed for 2 hours; 34.0 g of n-butyraldehyde was then added andallowed to react at 75° C. for four hours. The reactor contents was thenneutralized with sodium hydroxide to a pH of 12.5 and dumped into waterto cause polymer to precipitate. It was then filtered and dried as inExample 1 and found to have a Tg of 90.7° C. (versus 73° C. forconventional control PVB). IR spectroscopy results showed the presenceof COOH groups prior to neutralization with caustic and COO- peaks inthe resin after neutralization.

CONTROL EXAMPLE 1

This control Example illustrates the importance of low temperature informing ionomeric PVB using BSNA.

The procedure of Example 1 was repeated except that reaction temperaturewas kept at 16° C. (preparation of precursor) and in part B (preparationof ionomeric PVB) up until gel break occurred (the first appearance ofPVB particles) when the temperature was increased to and held at 85° C.for 4 hours. NMR analysis of the polymer product showed no evidence ofchemical substitution of the BSNA. This is believed due to the 85° C.high temperature portion of the reaction cycle.

The preceding description is set forth for purposes of illustration onlyand is not to be taken in a limited sense. Various modifications andalterations will be readily suggested to persons skilled in the art. Itis intended, therefore, that the foregoing be considered as exemplaryonly and that the scope of the invention be ascertained from thefollowing claims.

We claim:
 1. Polyvinyl butyral resin containing about 15 to about 30% byweight hydroxyl groups calculated as vinyl alcohol and chemicallycombined neutralized ionomeric groups present in amount sufficient to becapable of providing thermally reversible ionic cross-links.
 2. Thepolyvinyl butyral of claim 1 wherein said ionomeric groups being boundto oxygen atoms of adjacent precursor vinyl alcohol groups.
 3. Thepolyvinyl butyral of claim 2 wherein the ionomeric groups are boundthrough the reaction between an aldehyde group and two hydroxyl groups.4. The polyvinyl butyral of claim 2 containing up to about 15 mole %ionomeric groups.
 5. Polyvinyl butyral containing about 15 to about 30%by weight hydroxyl groups calculated as vinyl alcohol and chemicallybound neutralized ionomeric groups of the formula R--XYZ--M where R isaromatic, aliphatic or heterocyclic aldehyde, acid, acid chloride orisocyanate, provided that when R is aliphatic it has the configuration(CH₂)_(n) where n is an integer from 1 to 200; X and Y, which can be thesame or different, are substituents on the aromatic and heterocyclicforms of R and are H or C₁ to C₅ alkyl; Z is So₃ ⁻, COO⁻ or PO₄ ⁻³ and Mis a cation selected from alkali metals, alkaline earth metals andtransition metals selected from zinc, copper and manganese saidionomeric groups being present in amount sufficient to be capable ofproviding thermally reversible ionic cross-links.
 6. The polyvinylbutyral of claim 5 containing about 2 to 5 mole % ionomeric groups. 7.The polyvinyl butyral of claim 5 where R is aromatic aldehyde and Z isSO₃ ⁻.
 8. The polyvinyl butyral of claim 7 containing 2 to 5 mole %ionomeric groups wherein M is Na⁺.
 9. Polyvinyl butyral thermallyreversibly cross-linked through ionomeric bonds and containing about 15to about 30% by weight hydroxyl groups calculated as vinyl alcohol. 10.The polyvinyl butyral of claim 9 wherein said ionomeric bonds aredeveloped between ionomeric groups bound to oxygen atoms of adjacentprecursor vinyl alcohol groups.
 11. The polyvinyl butyral of claim 10wherein the ionomeric groups are bound through the reaction between analdehyde group and two hydroxyl groups.
 12. The polyvinyl butyral ofclaim 10 containing up to about 15 mole % ionomeric groups.
 13. Thepolyvinyl butyral of claim 12 wherein the ionomeric groups have theformula R--XYZ--M where R is aromatic, aliphatic or heterocyclicaldehyde, acid, acid chloride or isocyanate, provided that when R isaliphatic it has the configuration (CH₂)_(n) where n is an integer from1 to 200; X and Y, which can be the same or different, are substituentson the aromatic and heterocyclic forms of R and are H or C₁ to C₅ alkyl;Z is SO₃ ⁻, COO⁻ or PO₄ ⁻ ₃ and M is a cation selected from alkalimetals, alkaline earth metals and transition metals selected from zinc,copper and manganese.
 14. The polyvinyl butyral of claim 13 containingabout 2 to about 5 mole % ionomeric groups.
 15. The polyvinyl butyral ofclaim 14 wherein the bonds are developed through the alkali metalsulfonate salt of an aldehyde.
 16. Polyvinyl butyral containingchemically combined, neutralized ionomeric groups and about 15 to about30% by weight hydroxyl groups calculated as vinyl alcohol, saidpolyvinyl butyral having been polymerized an situ with but afterformation of modified polyvinyl alcohol containing up to about 10 mole %ionic sulfonated benzal groups.
 17. The polyvinyl butyral of claim 16wherein the ionic groups are 2-formyl benzene sulfonic acid.
 18. Partialpolyvinyl butyral containing 65 to 95 weight percent vinyl butyralunits, 15 to 30 weight percent hydroxyl groups calculated as vinylalcohol and neutralized ionomeric groups chemically bound onto the chainbackbone.
 19. The partial polyvinyl butyral of claim 18 wherein theionomeric groups are bound to oxygen atoms of adjacent precursor vinylalcohol groups.
 20. The partial polyvinyl butyral of claim 19 whereinthe ionomeric groups are bound through the reaction between an aldehydegroup and two hydroxyl groups.
 21. The partial polyvinyl butyral ofclaim 19 containing up to about 15 mole % ionomeric groups.
 22. Thepartial polyvinyl butyral of any of claims 18, 19, 20 or 21 wherein theionomeric groups have the formula R-XYZ-M where R is aromatic, aliphaticor heterocyclic aldehyde acid, acid chloride or isocyanate, providedthat when R is aliphatic it has the configuration (CH₂)_(n) where n isan integer from 1 to 200; X and Y, which can be the same or different,are substituents on the aromatic and heterocyclic forms of R and are Hor C₁ to C₅ alkyl; Z is SO₃ ⁻, COO⁻ or PO₄ ⁻³ and M is a cation selectedfrom alkali metals, alkaline earth metals and transition metals selectedfrom the zinc, copper and manganese.
 23. The partial polyvinyl butyralof claim 22 containing about 2 to about 5 mole % ionomeric groups. 24.The partial polyvinyl butyral of claim 22 where R is aromatic aldehydeand Z is SO₃ ⁻.
 25. The partial polyvinyl butyral of claim 24 containing2 to 5 mole % ionomeric groups wherein M is Na⁺.